1. Field of the Invention
The present invention relates to a motor abnormality detection apparatus used for abnormality detection of a brushless motor and an electric power steering control system equipped with such a motor abnormality detection apparatus.
2. Description of the Related Art
Conventionally, brushless motors are used in electric power steering systems or the like. In such electric power steering systems or the like, it is necessary to always perform the detection of faults or failures such as a break or disconnection of a motor power line, etc., in order to prevent abnormality in steering assist torque, i.e., the output torque of a brushless motor.
In general, a brushless motor control apparatus performs arithmetic calculations such as the calculation of d-axis and q-axis (hereinafter called “dq-axis”) target currents based on a command torque, the detection of motor currents of respective phases (for instance, u phase, v phase and w phase), the dq conversion (hereinafter called “uvw to dq transformation) of currents, the calculation of current deviations, the calculation of command voltage values, dq inversion (hereinafter called “dq to uvw transformation”), and PWM control pattern outputs. The respective detected phase currents are converted or transformed from three phases into two phases (i.e., dq conversion or uvw to dq transformation), and are subjected to feedback control so that their d-axis component and q-axis component become equal to a d-axis target current and a q-axis target current, respectively.
Here, note that the d-axis component of a current means a reactive or wattless current. When the motor is a synchronous motor with a constant magnitude of excitation magnetic field, the q-axis component of a current supplied to the motor is proportional to the torque of the motor. Therefore, in the current feedback control, in case of the synchronous motor, it is generally controlled such that the d-axis component of the detected current becomes zero and the q-axis component becomes equal to a target value of the output torque.
For instance, in an apparatus disclosed in Japanese patent application laid-open No. 2000-184772, abnormality determination is performed by supplying a current to the d axis of a brushless motor.
In this apparatus, however, operation efficiency reduces due to the fact that a d-axis current, which is usually controlled to be zero, is supplied to the motor in order to detect abnormality or fault in the motor. On the other hand, if abnormality detection processing is carried out at constant time intervals to avoid the reduction in efficiency, there will be generated a delay in abnormality detection.